Typically, portable satellite terminals are used in Satellite News Gathering (SNG) and in military communication systems. Particularly in the latter case, it is important to achieve the right balance between antenna size (affecting portability), good performance and ease of setup.
Prior art auto-acquire systems for satellite terminals typically contain the following hardware and software elements:    1) Antenna positioners (i.e. for elevation, azimuth and polarization adjustment). The polarization angle may be adjusted by rotating the whole antenna but it is more common to rotate only the feed.
An important aspect of antenna positioning systems is an accurate indication of the current azimuth, elevation and polarization angle. Those data serve as feedback for the initial pointing in the satellite acquisition process. Such feedback is generally in the form of a suitable electrical quantity, such as voltage. There are several patents dealing with motorized antenna alignment; examples of these are U.S. Pat. Nos. 4,665,401, 4,907,003, 6,049,306, 6,937,119, 5,594,460.
The disadvantage of the prior art systems is the relatively low accuracy and resolution and the susceptibility to slippage or backlash, depending on the method of mechanical coupling to the sensors for azimuth, elevation and polarization angles.    2) A location determining device, typically a GPS receiver. This provides the terminal's longitude and latitude, which are used, in conjunction with the satellite data, to calculate the look angles for the initial pointing of the antenna. It would be advantageous to have alternate or back-up means for determination of the terminal's location and for inputting this data into the system in the event of GPS failure.    3) An indicator of signal strength, (e.g. a beacon detector or an AGC (Automatic Gain Control) circuit). In the prior art the indicator of signal strength is generally the final arbiter in the alignment, (e.g. U.S. Pat. Nos. 4,907,003, 6,049,306, 5,422,648, application US 20050248498, Canadian patent CA 1327076 and international patent application WO2005053093), however, depending on the accuracy of the initial pointing and the location of the chosen satellite, such systems may still lead to alignment on another satellite, spaced a small angle apart from the desired one. This emphasizes again the need for accurate sensors for the initial alignment. Even more importantly, it is also desirable to have means to validate alignment.    4) A “satellite recognizer” to detect satellite characteristics. A prior art example wherein a spectrum analyser is used to perform this function, is disclosed in WO 02078215. However, in that application the spectrum analyser and corresponding control software are located in a central station of a network of satellite terminals and the data for antenna positioning are distributed to a network of individual satellite terminals via a separate radio network. Further, such prior art portable terminals are not equipped with full-featured spectrum analysers. Thus there exists a need in the prior art for a high-performance, compact, low cost satellite recognizer concept that can be incorporated into portable satellite terminals.
Accordingly, it is an object of the present invention to provide improved satellite acquisition systems and software, having features that address the deficiencies of the prior art described above.